Question 1

What are Route Handlers in the App Router?

Accepted Answer

route.ts files exporting HTTP method functions to build API endpoints. They replace many Pages API routes. Can run on Node or Edge runtime. Good for webhooks, auth callbacks, and JSON APIs colocated with the app.

Question 2

When should you use a Route Handler vs a Server Action?

Accepted Answer

Route Handlers for public HTTP APIs/webhooks/clients; Server Actions for first-party UI mutations tightly coupled to forms/components. External mobile clients usually need REST/RPC endpoints. Browser form posts can use actions. Don't expose actions as a general public API without care.

Question 3

How do you read JSON body and query params in a Route Handler?

Accepted Answer

await request.json(); use new URL(request.url).searchParams. Validate inputs. Handle empty bodies. Return proper status codes. Prefer shared validation (zod) with the rest of the app.

Question 4

What are Edge vs Node runtimes for route handlers?

Accepted Answer

Edge is lighter/faster cold start with API limits; Node supports full Node APIs and heavier libraries. Choose Edge for simple auth/redirects/geo. Use Node for ORMs, file system, or native deps. Know compatibility constraints.

Question 5

How do you secure a webhook route handler?

Accepted Answer

Verify signatures, use secrets, reject replays, and keep handlers idempotent. Never trust raw body without verification. Log carefully without leaking PII. Return quickly and process async if needed.

Question 6

Can Route Handlers set cookies for auth?

Accepted Answer

Yes — use NextResponse and cookie APIs carefully with Secure/HttpOnly/SameSite. Coordinate with middleware and server components reading cookies. Be explicit about cookie paths and domains in multi-subdomain setups.

Route Handlers Next.js Interview Questions

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